Industrial technique



Dec. 22, 1970 T. P. M FADDEN ETAL INDUSTRIAL TECHNIQUE Filed NOV. 18, 1968 Z'P McFADDEN //Vl N70R$ R. MOE

EB. 8/0077 5) 9 A ATTORNEY United States Patent Office Patented Dec. 22, 1970 3,549,421 INDUSTRIAL TECHNIQUE Thomas P. McFadden, Brooklyn, N.Y., Rolf Moe, Scotch Plains, N.J., and Frank B. Sidoti, Brooklyn, N.Y., as-

signors to Burmar Chemical Corporation, Brooklyn,

N.Y., a corporation of New York Filed Nov. 18, 1968, Ser. No. 776,666 Int. Cl. B08b 5/00 US. Cl. 134-31 8 Claims ABSTRACT OF THE DISCLOSURE A technique for rapidly and thoroughly cleansing the interior surfaces of the trailers on tank-trucks, and the like. After the tank contents have been discharged, a hose is attached from a vapor generator mounted on the trailer to a tank storage volume inlet. A degreasing solvent (preferably a mixture of mineral oil and 1,1,1-trichloroethane) is vaporized in the generator and flows through the hose and into the storage volume, usually while the truck is enroute to a new destination. The solvent vapor reduces the viscosity of the residue adhering to the tank walls, enabling it to flow to the bottom of the tank for subsequent disposal. The tank, moreover, may be cooled by means of a water spray, for example, when the structure exceeds 80 degrees F.

BACKGROUND OF THE INVENTION (1) Field of the invention This invention relates to cleansing techniques and, more particularly, to methods and apparatus for cleaning the interiors of tank-truck trailers, and the like.

(2) Description of the prior art Tank-trucks frequently are required to make trips in which successive cargoes are in some way incompatible. For instance, an initial load might comprise a product that has a flammable or combustible solvent base. The next cargo might be an edible oil that can be destroyed or contaminated by residual traces of the solvent that remain in the tank.

To overcome this problem, two prior art techniques have been developed. These systems are called the sonic ray and vapor degreasing methods. Both methods are employed only at central cleaning yards or chemical plants. The sonic method involves a three-hour application of high frequency sound waves to a tank in order to degrease the interior fully. The vapor degreasing technique ordinarily is accomplished in about an hour, but uses a large, expensive quantity of trichloroethylene solvent.

Both of these methods, however, impose more subtle losses and inefliciencies than are apparent from the length of cleansing time or the volumes of solvent needed to achieve a satisfactory result. For example, a tank-truck after delivering a load must often drive a great distance in an empty condition to reach a cleaning station for degreasing before receiving a new cargo. This requirement is aggravated even further if the discharged cargo was a flammable substance. Ordinarily, a truck carrying a residue of this sort cannot travel to a destination over the most direct route. A more roundabout route often is required because bridge and tunnel regulations frequently prohibit the passage of vehicles in this sort of a condition.

Such unproductive use of equipment is expensive and wasteful. Consequently, a need exists to reduce the turnaround time imposed on tank-trucks through the need to clean the tanks in circumstances exemplified by the foregoing description.

SUMMARY In accordance with an aspect of the invention, cleaning apparatus is made an integral part of the tank-truck structure. In this way, the tank can be cleansed while the trailer is enroute to a new destination. This feature of the invention eliminates the inconvenient and wasteful requirement to return, usually by way of a circuitous route, to a central cleaning station.

A further aspect of the invention provides an improved solvent for stripping a tank while the trailer is moving. In this regard, any acceptable solvent, of which 1,1,1-trichloroethane is preferred, can be mixed with a fluid characterized by a high boiling point to provide a wet-bed. Mineral oil, mineral seal oil, or a chlorinated solvent that has a higher boiling point than the foregoing 1,1,l-trichloroethane can be mixed together and used in the vapor generator with exceptionally good results.

It has been found, moreover, that the invention is practiced best when the temperature of the tank is kept at less than degrees F. during cleansing. This particular feature of the invention is contrary to ordinary experience. For instance, in a vapor degreasing operation, it might be assumed that high tank temperatures will improve cleansing action by keeping the solvent in a vapor state and reducing the viscosity of the residue. It has been found, however, that the opposite situation appears to be true. The cleansing method and apparatus function best at less than 80 degrees F. On hot days, this temperature can be maintained, for example, by hosing the exterior of the tank with cold water.

Thus there is provided in accordance with the invention an improved method and apparatus for cleansing surfaces, of which tank trailers, tank ships, storage tanks and the like are typical. For a more detailed understanding of the invention, attention is invited to the accompanying drawing and the following description.

BRIEF DESCRIPTION OF THE DRAWING The sole figure of the drawing shows a schematic diagram in broken section of a tank-truck illustrating one embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS An illustrative embodiment of the invention is shown in the drawing. For instance, a tank truck of the sort used to transport fluids over highways and the like comprises a tractor 10 coupled to a tank trailer 11. The trailer preferably has a fluid-tight tank 12 supported by a chassis or frame 13 on which wheels 14 and retractable landing gear 15 are mounted. The landing gear 15 frequently is extended in order to support the trailer when it is uncoupled from the tractor 10 between trips.

The tank trailer 11 further includes a drain pipe 16, preferably in fluid communication with the lowermost point of the tank interior. The drain pipe 16, moreover, is equipped with a manually controlled valve 17, and optionally, a pump (not shown) to allow the contents of the tank 12 to be discharged. Additionally, the tank 12 is equipped with one or more manholes 20 on the upper surface to allow the tank to be filled with fluid or entered for inspection, as the case may be.

In accordance with one feature of the invention, a sol vent vapor generator 21 is mounted on the trailer 11. Alternatively, the generator 21 may be mounted on the tractor 10. It is important to note that in the illustrative embodiment of the invention, the generator is secured in a convenient location on the tractor-trailer combination so that it can be operated while the trailer is in motion, as described subsequently in more complete de- 6 tail. As shown, the generator 21 is secured to the rearmost portion of the frame 13.

The vapor generator 21 (not shown to scale) includes a lower reservoir 22 and a water filling line 23 for replenishing the reservoir 22 with heating water 24, as subsequently described more completely. A valve controlled drain line 25 also is provided to enable the water 24 to be drawn from the reservoir 22, when required.

A vaporizing unit 26 is secured to the frame 13 by supports 27 that are fixed perpendicular to the major dimension of the frame 13. Typically, a fifteen gallon vaporizing unit is adequate for cleaning a 6,000 gallon tank trailer.

A heating coil 30, shown for illustrative purposes as energized by a battery 31, is positioned within the unit 26 to vaporize the volatile material with a charge of solvent 32. A switch and timer 33 is set to complete the circuit for a heating element 34 through the battery 31 for a predetermined time. The water 24 in the heating coils absorbs heat from the element 34 and circulates through natural convection or water pump. The water 24 transfers heat to the solvent 32 for a time determined by the timer 33.

Water drawn from the reservoir drain 25 can be used to refill the heating coil 30 through a filling cap 38 on a portion of the coil 30 that is external to the unit 26, as required.

There are many alternative techniques for heating the solvent 32, For example, the water 24 in the coil 30 can be heated by the exhaust gases from the engine of the tractor 10. Hot water from the tractors cooling system also can be used, as well as bottled gas or an ordinary gasoline burner to heat the water 24.

The upper end of the vaporizing unit 26 has a filling cap 35, a vapor outlet 36 and a pressure relief valve 37. It has been found, for example, that the fifteen gallon capacity vaporizing unit 26, when filled with about four to six gallons of Chlorothane V.G. solvent and heated to about 190 degrees F., raises about 20 p.s.i. pressure in the unit. In general, 20 p.s.i. vaporizing unit pressure is an optimum value for the technique. The pressure relief valve 37 can be set to open at a slightly higher pressure in order to maintain the optimum pressure. A range of about five to fifty p.s.i. has been found adequate for the practice of the invention, although other vapor pressures also can be used. A flexible vapor transfer hose 40- connects the vapor outlet 36 on the vaporizing unit 26 to an inlet 41 on a threaded manhole cover 42, or any other threaded opening on the top. In order to facilitate securing the manhole cover 42 in place in the manhole 20 without twisting the hose 40, the hose is connected to the inlet 41 through a quick closing or snap-on coupling 43. In this regard, the manhole cover 42 is secured in place and the hose 40 then is connected to the inlet 41 through the coupling 43.

The manhole cover 42 also has a pressure relief valve 44 to control vapor pressure within the tank 21 during cleanings. The valve 44 is set to open when tank pressure reaches a value of approximately 3 to 5 pounds per square inch (p.s.i.).

A pair of convex discs 45 extend from the inlet 41 through the manhole cover 42 to protrude into the tank and distribute the solvent vapor during operation, as d? scribed subsequently.

In operation, the valve 17 in the tank drain pipe 16 is opened and the pump (not shown) is operated to discharge, insofar as possible, the tank contents. The heating coil 30 is filled with water drawn from the drain 25 on the reservoir 22. The vaporizing unit 26 also is filled with about one and one-half gallons of solvent for every 2,000 gallons of tank volume, or about four to six gallons of solvent for the average 6,000 gallon tank. The heating element 34 is energized and the solvent 32 is heated until it vaporizes and flows through the hose 40, the inlet 41 and the inverted T 45 into the tank 12.

Preferably, a substance known by the trademark Chlorothane V.G.- (a mixture of 1,1,1-trichloroethane and minute quantities of nitromethane and dioxane) has provided exceptional results when used with the apparatus shown in the drawing.

It will be recalled that 1,1,1-trichloroethane was described as the preferred solvent. The physical and chemical properties of this substance are described in more complete detail in the brochures Dow Chlorothane V.G., published by the Dow Chemical Company and Vapor Degreasing with Tri-Ethane published by P.P.G. Industries, Chemical Division, One Gateway Center, Pittsburgh, Pa.

The invention, however, is not limited to the application of a specific solvent or even a specific group of chlorinated hydrocarbon solvents. Typical of the many possible solvents are a fifty percent by volume mixture of methylene chloride and the aforementioned Chlorothane V.G. A mixture of 90% by volume-of methylene chloride and 10% by volume of methanol also is satisfactory.

Of course, before heating the solvent 32, the vapor transfer conduit or hose 40, formed preferably of stainless steel, should be coupled to the coupling 43 in the manhole cover 42, which previously had been secured in the manhole 20. The timer in the switch and timer unit 33 then can be set to supply adequate heat to the coil 30 for about ten minutes. Ten minutes has been found to be a more than sufiicient length of time to cleanse thoroughly a 6,000 gallon tank.

If the ambient atmospheric temperature warms the tank structure to degrees F. or more, the outer surface of the tank can be hosed down with cold water during degreasing to enable the cleaning to proceed in an optimum manner. A special feature of the invention enables the driver of the tank-truck to drive the vehicle to a new destination to pick up a fresh cargo that even may be incompatible in some way with the former contents of the tank 12. The truck only need be stopped to discharge the solvent and residue mixture through the drain line 25 and uncouple the hose 40 from the manhole cover 43 before accepting a new load. The timer 33 automatically stops the vaporizing process in the unit 26 at the appropriate time, thereby relieving the driver of the further responsibility to turn off the degreasing system. On hot days, the exterior of the tank can be sprayed with water and then driven, relying on evaporation to cool the tank to less than 80 degrees F.

Clearly, this technique also eliminates the exceptionally wasteful requirement to drive an empty truck through a circuitous route to some central degreasing station before accepting a new cargo.

If the vaporizing unit 26 is to be operated while the truck is in motion, it has been found beneficial to use a wet bed mixture. A mixture of this character is, in general, a combination of a very high boiling point liquid and a solvent chosen, for example, from the group hereinbefore described. Typical of these mixtures are the aforementioned 1,1,1-trichloroethane and mineral oil. 1,1,1- trichloroethane and mineral seal oil having a boiling oint of about 500 degrees F. (a proprietary roduct sold by the American Mineral Spirits Company) as well as 1,1,1- trichloroethane and a higher boiling point point solvent (as, for example, perchloroethylene with a boiling point of about 250 degrees F.) also have been found satisfactory in this connection. Thus, by mixing the solvent in any desirable proportion with a liquid that has a boiling point preferably higher than the maximum temperature of the heating coil 30, the vaporizing unit 26 is protected from damage should the switch and timer 33 fail to deactivate the coil before all of the solvent has vaporized.

It will be recalled that the sonic ray degreasing technique of the prior art requires about three hours to clean a 6,000 gallon tank. The Detrex system, moreover, consumes sixty gallons or more of cleaning fluid. Actual test of the system under consideration have been conducted, however, with the following results.

A 6,000 gallon compartmented tank-truck carrying a difiicult-to-remove brown lacquer was treated in the foregoing manner while stationary with a 1,1,1-trichloroethane vapor and, within six minutes, compartment number 1 was in spotless condition. In compartment number 2 the first cleaning was incomplete due to very unclean surfaces caused by improper tank venting. The cleansing process was repeated and good results were obtained. Compartment number 3 was cleansed thoroughly in eight minutes. A total of 4 /2 gallons of solvent was required to clean the entire 6,000 gallon tank.

During this cleansing operation, the solvent was maintained at about 190 degrees F. and 20 p.s.i. in the vapor generator.

It will be apparent to those skilled in the art that the foregoing invention is subject to many modifications. Thus, the representative embodiments illustrated above are not to be considered as limiting the appended claims.

We claim:

1. A method for cleaning a tank-truck comprising the steps of coupling a conduit between a vapor generator on the tank-truck and the tank to establish free communication therebetween, heating said vapor generator, flowing a vapor through said conduit and into said tank to cleanse the tank interior, and terminating said flowing vapor after said tank interior is clean.

2. A method according to claim 1 comprising the further steps of draining condensed vapor from said tank and uncoupling said conduit between said generator and said tank.

3. A method according to claim 1 comprising the further step of cooling said tank to less than 80 degrees F. when said vapor is flowing thereinto.

4. A method for cleaning a tank-truck comprising the steps of mixing a chlorinated solvent with a mineral oil,

pouring at least some of said mixture into a vapor generator on the tank-truck, connecting a conduit between said vapor generator and the tank to establish vapor communication therebetween, heating said mixture in the vapor generator, and establishing a pressure difference between said vapor geneartor and the tank.

5. A -method according to claim 4 wherein said mixing step comprises mixing 1,1,1-trichloroethane and mineral seal oil.

6. A method according to claim 4 comprising the further step of terminating said heating step at some predetermined time.

7. A method according to claim 4 comprising the further steps of draining condensed vapor from said tank and disconnecting said conduit.

8. A method according to claim 4 wherein said pressure difference is established while the tank-truck is in motion.

References Cited UNITED STATES PATENTS 2,092,321 9/1937 McFadden 134-40XR 2,348,465 5/1944 Geiringer 13422XR 2,561,158 7/1951 Tuttle 134--40UXR 2,838,458 6/1958 Bachtel 134-40XR 2,866,726 12/1958 Vance 134-40XR 2,969,328 1/1961 Ellenson et al. 134-38UX 3,188,238 6/1965 Lyon l34-37XR 3,042,553 7/1962 Kearney et al. 134-30XR 3,483,092 12/1969 Young 13430XR MORRIS O. WOLK, Primary Examiner J. T. ZATARGA, Assistant Examiner US. Cl. X.R. 

